Although contraception allows women to delay childbirth, stop unwanted childbearing, and postpone childbirth, not all contraception is equally effective, equally easy to access, or equally easy to use. Due to heterogeneity in women's contraception opportunities and choices, in the effectiveness of the contraception used and even in luck, women differ in both their birth intervals and their age at first childbirth. We explore this heterogeneity, theoretically, incorporating contraception effectiveness and uncertainty (along with potential earnings, contraception costs, and net child benefits) into a potential mother's childbearing decisions. Empirically, these factors are incorporated into a first hit time duration model, focusing on time to first birth, estimated with data from the Democratic Republic of Congo. The results provide nuanced insights into the income-fertility puzzle. Our evidence suggests that educated women start childbearing later, and are better able to use contraception, even less effective contraception. Thus, there are education-related heterogeneities in contraceptive effectiveness. Further, we find that women using more effective contraception start childbearing at a later age, as do women with better access to contraception. Both improved female education and improved access to modern contraception have the potential to hasten the fertility transition in the Democratic Republic of Congo.